Low grid current glow tube



May 7, 1940. D. D. KNOWLES LOW GRID CURRENT GLOW TUBE Filed Dec. 9, 1936 m. M WK m m0 m m; %m m 6 flaw 49/2 a4 fiaa a ww l| a r 7 0 H v 5 a a 7 a 3M 4 4 a z WITN ESSES: WW

Patented May 7, 1 940 I LOW GRIDICURRENT crow TUBE Dewey D. Knowles, Wilkinsburg, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa.,' a corporation of Pennsylvania Application December 9 1936, Serial No. 114,967

2 Claims. (01. 250-27) My invention relates to discharge devices and especially to grid controlled glow tubes.

. An object of my invention is to provide a tube having efiective control by a grid with'very small grid currents.

Other objects and advantages of my invention will be apparent from the following description taken in conjunction with the drawing, in which:

Figure 1 is a sectional view of a tube embodying my invention; 1 i

I Fig; 2 is a top planview of the grid in Fig. 1;'

Fig. 3 is a sectional view of a modification of Fig. l; and, I I

Fig. 4 is a sectional view of the cathode enclosure of Fig. 3.

In the construction of grid controlled glow and are discharge tubes, one of the principal problems is to so design the grid that the current flowing to it at the critical starting point is very small. The ideal tube would, of course, be one in which this current is zero as in high vacuum or hard tubes. The grid current in a gas filled tube,-assuming zero grid emission is that due to ions and electrons that arecollected by the grid from the gaseous medium around it which is slightly ionized by the pre-ignition or threshold discharge just preceding the are or glow discharge. In gas filled tubes, especially those for heavy current and voltage industrial uses, the size of the electrodes have been increased in order to provide higher ratings. With the increased size of the grid, the grid current necessary at the critical starting point has also become considerably greater. The increase in size of the grid is also the resultof trying to prevent the discharge occurring around the grid by completely isolating the anode from the cathode by the grid and thus compelling the discharge to take place through the meshes or other opening of the grid.

In the. prior art this isolation by the. grid has been taken care of in two ways. I In one instance the grid extends completely across the tube between the glass'walls, so that there is no other path from the cathode to the anode thanthrough the grid openings. This structure is objectionable because the grid touches the glass walls and cannot beoutgassed, because the heat treatment would damage the glass walls.

Another modification has been to surround both the cathode and the anode with a cylindrical grid having a perforated or mesh partition between the anode and cathode. This structure, since it encloses both the cathode and the anode, is very large and because of its large size requires excessive grid current.

According to my invention, I provide an enclosure about the active portion of the cathode" with a limited opening facing the other main elec-= trode. tive charge or potential relative to the cathode, so that the electrons must pass through the opening to the anode. The control grid may now be made of very small size adjacent to or covering the opening. Because of its small size, tliegrid current will be kept very small. Of course, I also contemplate that the anode may also be enclosed, if desired, instead of or in addition to this enclosure about the cathode. My preference, how.- ever, is for such an enclosure or guard electrode about the cathode. l 1

In Fig. l is disclosed a preferred embodiment of'my invention comprising the container ii] having a gaseous medium II which may beof any of the noble gases, such as neon or argon,'or. it may be of mercury vapor. The'cathode I2 is preferably of the directly heated type although the indirectly heated type may be used. This cathode-is preferably coated with the electron emitting coating, preferably including barium and strontium oxides. This cathode also preferably has the lead wires l3 supporting it from the reentrant press M. The anode I5 is preferably supported from a press l6 located at the opposite end of the tube from the cathode press 14.

Around the cathode I2, I provide an enclosure 11 that preferably encloses the effective area of the cathode [2, except for an opening H3 in this enclosure facing the other main electrode, namely,

This enclosure is preferably at a negathe anode 15. This enclosure I! can be supported very conveniently from the press 14 by the band l9 and this enclosure may have a separate lead passing through any convenient portion of the tube wall including the press l4. Adjacent the opening I8, I preferably provide a grid structure 2|. As disclosed in Fig. 2 this grid structure preferablycomprises an annular ring 22 having bars 23 extending thereacross. These bars may be kept in place by tabs 24 attached to the ring 22 or by any other convenient supporting means. A preferred material for these bars is graphite or carbonized nickel because this material is nonemissive even when hot. In place of these bars a material having a mesh form or other perforations may be utilized; In any case the size of the grid proper is very small because it is accommodated to the limited opening 18 which would probably be about /2" in diameter.

This grid may be conveniently supported in position by wires 25 which may extend to one of the presses such as I6. A grid lead 26 may pass through the tube at any convenient position. In operating the device I preferably put a charge or potential on the cathode enclosure I! ,that is more negative than the cathode l2 in order that the electrons will necessarily pass through the opening H! to reach a more such as the anode l5.

In Fig. 3, I disclose a further modification in which my invention is applied to an anode concentrically or radially placed in respect to the cathode. The container ID has its gaseous medium H as in. Fig. 1. I disclose, however, in this embodiment only a single reentrant press 30 for the support of the electrodes although, of course,

a other presses may be used. The cathode 3| is illustrated as the directly heated type and is placed in an axial position. The enclosure for the cathode in this case is approximately that of a closed end cylinder cut in half andseparated for the emission of electrons. The lower half cylinder 32 may be supported by a lead 33 from the press 30. The upper half cylinder 34 may be supported from the lower portion by bars 35 welded or otherwise secured to the two parts. The upper portion 34' also preferably has an extension 36 supporting an insulating plate 31 such as glass. The space 38 between the two portions of the enclosures 32 and 34 is surrounded by a mesh or perforated cylinder 39 to act as a control grid. This perforated cylinder is supported from the press 30 by the lead 46 and the standard 4|. It is preferred tohave the grid fixed in position by extending certain standards 42 from the upper portion of this grid structure to be secured in the insulating plate 3! by fusion thereto at 43.

An anode 44 of any desired shape and configuration surrounds this assembly of electrodes and preferably has a supporting lead 45 from a band 46 surrounding the press 30. An anode lead 4! positive electrode may extend through the tube wall'at any desired location including that of the press 30.

It will be noted that in this case also, I have utilized a grid area small in size and also material for controlling the electron emission from the opening'38 of the cathode enclosure. 1 In this case also I prefer to put a charge on thecathode enclosure that is more negative in respect to the a cathode.

It is obvious that many changes may be made in the size, shape and arrangement of the various elements and also in their combinations Accordingly, I desire only such limitations to :be

imposed upon the following claims as are neces sitated by the prior art.

I claim as my invention:

1. In combination, a discharge devicecomprising an envelope containing a gaseous atmosphere, an electron-producing electrode, an enclosure thereior having an opening, an electron collecting electrode,an electrode controlling the passage of electrons from said opening to saidyelectronj collecting electrode, and means for impressing upon said enclosure a negative continuous electrical potential relative to said electron-producing electrode, the other said electrodes being out side the compass of the walls of said enclosure. 2. A discharge device'comprisin'g a, container having a gaseous atmosphere therein, an anode, a cathode, a grid interposed between said cathode and anode and an enclosure for said cathode having an openingadjacent said grid, and means for imparting to said enclosure a definite continuous electrical potential of substantial magnitude.- relative to said cathode, said grid and anode bing outside the compass of the Walls of said en closure. 7

DEWEY D. KNOWLES. 

